The calendar says it’s the first of August. But an unforgiving early wave of heat means that California’s landscape feels as dry as September, igniting a deadly wildfire season up and down the state.

Hot and dry as a powder keg, recent weather has accelerated the normal drying of western landscapes, turning vegetation into kindling, say weather experts. Even nights are warm.

“Fuels are really really dry. It’s closer to what we should get by late summer or early fall,” said professor Craig Clements, director of the Fire Weather Research Lab at San Jose State University.

The “fuel moisture level” of shrubs, trees and grasses — the single largest factor for how primed an area is to burn — is below average throughout the state, including the Bay Area, data shows.

Normally, the mean fuel moisture content of vegetation in Mendocino County, where the Mendocino Complex fires are raging, is 12.4 percent; now it’s less than 11 percent. In Shasta County, the site of the huge Carr Fire, moisture content has fallen from an average of 9.4 percent to 7 percent, according to a web-based climate tool, developed with Google by John Abatzoglou, associate professor of geography at the University of Idaho. The “Climate Engine” tool assesses how wet or dry a landscape’s vegetation is — and how likely it is to ignite and carry a fire.

The Bay Area’s vegetation also is dry, it shows. In Santa Clara County, moisture content at this time of year normally is 10.59 percent — now it’s 9.3 percent; in Alameda County, normally 11.5 percent, it’s fallen to 10.6 percent; in Contra Costa County, normally 11.45 percent, it’s nine percent; and San Mateo County has fallen from an average of 14.5 percent to 13.8 percent.

But that’s just part of the story: Nights have been warm, as well, with everywhere from Eureka to Death Valley above normal. At San Jose Airport, July’s average low temperature is 58 degrees; last month it was 61.

“When it’s a couple degrees warmer overnight, you already have a head start on the next day,” said Steve Anderson, meteorologist with the National Weather Service in Monterey.

The Golden State always has been a thirsty land — even before you factor in the hazards of a worsening climate. With a Mediterranean climate, nearly all of our rain falls from November to April. And last winter’s precipitation was below normal. By August, we’ve gone four months without receiving a drop of rain.

But a persistent high pressure system makes it feel like a training ground for Hades, unless you live in foggy San Francisco.

Nowhere has this month’s heat been more brutal than in Death Valley, where July’s average high reached 121 degrees – four degrees above the annual average.

All over the state, the departure from average temperatures ranges from two to eight degrees. Down in Riverside County, alfalfa grower Grant Chaffin reported that crops are being hit with “summer slump,” with high nighttime temperatures causing yields to drop by half, according to the California Farm Bureau.

Only San Francisco and parts of Marin County are celebrating summer-as-usual.

Research by a team lead by Abatzoglou shows that these hot conditions, which dehydrate our vegetation, are contributing to fire risk.

In recent years, human-caused increases in temperature have dried out western U.S. forests, accounting for about half of the increase in tinder-dry conditions, he found. The other half of problem is driven by natural temperature variations.

Climate change is projected to increase to potential for fires across this western landscape, according to his research. It estimates that human-caused climate change contributed to an additional 10.5 million acres of high-risk forest fire areas between 1984–2015.

“The effect is one of warming — and also decreases in humidity,” he said.

Additionally, there is growing recognition that warming temperatures can worsen a drought.

A Stanford team previously reported that the conditions behind our 2011-2017 drought — a high pressure system parked over the Pacific Ocean, diverting storms away from California — are much more likely to occur amid concentrations of greenhouse gases.

Scientists warn that there could be be even worse heat waves, droughts and fire risks in the future — as the planet endures increasingly volatile weather patterns that will make dry places, like much of California, dangerously drier.

Lisa M. Krieger is a science writer at The Mercury News, covering research, scientific policy and environmental news from Stanford University, the University of California, NASA-Ames, U.S. Geological Survey and other Bay Area-based research facilities. Lisa also contributes to the Videography team. She graduated from Duke University with a degree in biology. Outside of work, she enjoys photography, backpacking, swimming and bird-watching.